1. Field of the Invention;
The present invention relates to an indicating device for a tuning apparatus. More specifically, the pressent invention relates to a device for indicating a tuned frequency in a tuning apparatus employing a voltage controlled variable reactance device.
2. Description of the Prior Art;
Recently an automatic tuning apparatus employing a voltage controlled variable capacitor has been widely used in radio receivers, television receivers and the like. Such a voltage controlled variable capacitor uses a capacitance formed at a barrier portion of a diode, variable as a function of a reverse voltage applied thereacross and is known as a variable capacitance diode. In such an automatic tuning apparatus, it is necessary to provide a voltage supply capable of providing a voltage variable as chosen in response to manual operation, which causes a capacitance with which the tuning apparatus selects a desired tuning frequency and thus selects a desired transmitting station. It is well known that such a voltage is closely related with the tuning frequency and thus the selected transmitting station.
In the receiving equipment employing such a tuning apparatus, it is most preferred to provide an indicator which indicates a tuned frequency and/or selected transmitting station. For that purpose it would be obvious to those skilled in the art to employ a visual indication by means of a volt meter for indicating the voltage applied to the voltage controlled variable capacitance diode in terms of a tuned frequency and/or a selected transmitting station. Nevertheless, such an indication by means of a volt meter is disadvantageous and less preferred in that a response rate thereof is slow and design of the receiver is limited thereby, the structure thereof is not very shock-proof and reliability thereof is small. It is desired that a preferred indicator is provided which is suitable for use in a receiver employing a tuning circuit using a voltage controlled variable reactance device, such as a voltage controlled variable capacitor. The present invention was completed to achieve such a purpose.
One type of such a voltage supply for providing a voltage variable in response to manual operation to a variable capacitance diode comprises a capacitor and a charging/discharging circuit therefor, a voltage across the capacitor, as selected in response to a tuning output, being applied to the variable capacitance diode. More specifically, the capacitor is charged or discharged by the charging/discharging circuit in response to manual operation until a voltage across the capacitor causes capacitance in the diode with which the tuning circuit tunes to a given frequency to provide a tuning output therefrom when the charging/discharging circuit is disabled to discontinue to charge or discharge the capacitor, so that the voltage thus provided across the capacitor remains the same. If another tuning frequency is desired, the charging/discharging circuit is again enabled through manual operation and the abovementioned operation is repeated until another frequency is tuned.
A voltage storing device of interest in connection with the present invention is disclosed in U.S. Pat. No. 3,753,110, issued Aug. 14, 1973 to Hironosuke Ikeda et al. and assigned to Sanyo Electronic Co., Ltd. the same asssignee as that of the present invention. As set forth in the referenced patent, Professor Takehiko Takahashi and Assistant Professor Osmu Yamamoto, Technological Department of Nagoya University, announced their study on the electrochemical potential memory device by the use of a solid state electrolyte at the 22nd annual assembly of Japan Chemical Association held on April 5th to 7th, 1969. Briefly stated, this device comprises an Ag elecrode as a cathode, an Ag-Te alloy electrode as an anode, and a solid state electrolyte having high ion conductivity, such as RbAg.sub.4 I.sub.5 sandwiched between both electrodes. When a DC voltage is applied to the device so that the Ag electrode may be negative, a portion of Ag contained in the Ag-Te alloy electrode migrates over to the Ag electrode, resulting in a decreased activity of Ag in the Ag-Te alloy, and thus an increased potential difference between both electrodes. The inventors of this device termed this state of operation as "charging". When the polarity of the applied DC voltage is reversed to that of the former case, Ag is refilled into the AG-Te alloy, resulting in the decreased potential difference and returns to the initial value eventually. The inventors of this device termed this state of operation as "discharging". Study disclosed by the inventors of this device indicates that the electromotive force generated by the abovementioned charging or discharging current can cause linear change to some extent with respect to the charging or discharging time. Thus this device makes it possible to effect write-in and non-destructive read-out operation while preserving relatively linear relation between the charging or discharging time and terminal voltage, and in addition, it can hold the memory condition for a relatively longer period of time. The referenced patent further discloses an improved electrochemical potential memory device. More specifically, FIG. 6 of the referenced patent shows an improved electrochemical potential memory device for eliminating the IR drop across the resistance in the electrolyte and the overvoltage caused by dissolution or deposition of Ag, which is basically characterized by the provision of an auxiliary cathode that comprises an output terminal for detecting the potential separately from the abovementioned cathode available for the input terminal for the current conduction. In view of these advantageous characteristics of the abovementioned memory device, it is possible to utilize this device as a voltage source for providing a voltage variable in response to manual operation to a voltage controlled variable reactance device employed in an automatic tuning apparatus.
It is pointed out that the present invention is applicable to a tuning apparatus employing a voltage controlled variable reactance device which is supplied with a voltage from any type of voltage source.